This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
To satisfy the ever-increasing demand from networked society either on huge traffic volume or very low latency, it has been agreed that two strategies shall be applied, one of which is to densify wireless networks (that is, to deploy more access nodes (ANs) in the wireless networks) and the other of which is to exploit very high frequency spectrum (such as the frequency range of tens of GHz).
However, on one hand, the propagation, penetration and diffraction attenuations at such high frequency spectrum are much higher. On the other hand, the receiver antenna aperture which characterizes how well the receiver can collect electromagnetic energy from incoming electromagnetic waves is frequency dependent. Due to these facts, the link budget would deteriorate dramatically for the same link if said high frequency spectrum is used instead of the conventional low frequency spectrum. To combat this disadvantage, BF technology has been applied in order to compensate for the deteriorated link budget at the high frequency spectrum.
FIG. 1 is a diagram illustrating a BF procedure according to the prior art, which generally comprises a beam sweeping stage (denoted as “sector level sweep” in the figure) and a beam refinement stage (denoted as “beam refinement” in the figure) followed by a beam tracking stage (not shown in the figure). During the beam sweeping stage, a pair of wireless communication devices (for example, an access node (AN) and a terminal device), between which the BF procedure is performed, transmit BF training sequences to each other and receive corresponding feedback information from each other at a low data rate to determine initial antenna system setting for both transmission and reception. Then, it proceeds to the beam refinement stage, where the antenna settings are further tuned to narrow the wide beam formed in the beam sweeping stage, thereby achieving an improved BF gain which enables high-quality and high-rate communications between the pair of wireless communication devices. Next, during the beam tracking stage, the narrow beam formed in the beam refinement stage is tracked to keep the refined antenna settings up to date, as the channel condition between the pair of wireless communication devices changes over time (for example, due to the mobility of the terminal device). More detailed description for the prior art BF procedure can be found in for example Institute of Electrical and Electronics Engineers (IEEE) 802.11-10/0433r2.
As a first possible implementation, the BF procedure may stay in the beam tracking stage after previous traffic data has been transmitted between the pair of wireless communication devices and may thus be always ready for forthcoming traffic data transmission (that is, there is no need to go through the beam sweeping stage and beam refinement stage again for the forthcoming traffic data transmission).
Alternatively, as a second possible implementation, the BF procedure may be terminated after previous traffic data has been transmitted and may be restarted for forthcoming traffic data transmission (that is, it is necessary to sequentially go through the beam sweeping stage, the beam refinement stage and the beam tracking stage once more whenever new traffic data is to be transmitted).
As compared with the second implementation, the first implementation might cause ineffective power consumption and signaling overhead for tracking the narrow beam formed in the beam refinement stage after the previous traffic data has been transmitted, in case there is a large time interval between the previous and the forthcoming traffic data transmissions.
On the other hand, in case the time interval between the previous and the forthcoming traffic data transmissions is relatively small, the second implementation would cause an intolerable latency for the forthcoming traffic data transmission.